Lightweight mineral material



Oct. 21, 1941.

P, s. DENNING LIGHTWEIGHTMINERAL MATERIL Filed oct. 25, 1937 52x/671507 x fau Z j en 7?. '72

thereofon the surface of the granules. Therev`upon the granules are heated to temperatures Peienred oec 2 1, 1941 UNiT-ED STATES PATENT oFFicE 2,259,879

rmn'rwarcn'r MATERIAL Pani s.. Denning, Juliet, ni., einer ie F'. E.

Schundier at Co., Inc., Joliet, lli., a corporation of AIliinois Appi'ieeiien oeieber z5. 1931, seein; No. 170,990 l (CL :i1-7o) i onine. This invention relates te lightweight minerai materials, and among other objects aims tol reinforce or strengthen fragile lightweight minerals so as to en able. them to vwithstand hard usage such as is encountered in mixing the same as an aggregate in concrete.l

The nature of the 'invention may be readily understood by reference to one illustrative embodiriient thereof,I described in the following specication a'nd illustrated in the accompanyii'i'gdrawing.'.

`In the drawing the figure represents a ldiaillustrating one method of fmaking the material. v

Exfoliated vermiculite isone example of a lightweight mineral material whose qualities are substantially impaired when subjected to rough' handling such as is encountered in the preparation of ylightweight". concrete.\ Exfoliated vermiculite yis an alteration product of certain micaceous minerals ofthe biotite type, which ex` foliate -or expand to many times` their original size uponv theapplication -of heat to'produce a lightweight granular mineral material which possesses aV high insulating efiiciency. It comprises numerous highly polished laminae which separate slightly upon exfoliation. It is semi-plastic or compressible in a direction perpendicular to the laminae and tends to split along the cleav- 118e planes when subjected to severe handling.

I thereby causing the residue to travel to and con- Otherwise its light 'weight and other qualitiesv make it an ,ideal aggregate for lightweightl concrete.-

. 1 have discovered that exfoliated vermiculite, lightweight slag, and other friable or soft lightweight mineral materials maybe toughened ad- 'equately without objectionable increase in weight or loss of insulating eiiiciency by an inexpensive treatment which .reinforces the exterior or surface of the granules of' material; Such toughening is provided in the [present instance by forming an insoluble mineral glaze or coating onthe granules. In treating exfoliated vemiculite, for

example,v according to the present process, the

granulesare mixed with a liquid coating forming y v, material and then dried to cause the liquid to' evaporate, thereby effecting a migration of the coating forming ymaterial to and concentration -to convert the coating forming material into a hard reinforcing coating or glaze.

I used as a coating material. It is mixed withv phia Quartz Co.

a soda to silica ratio of about 1 to 31A, quite'- satisfactory. A relatively high silica content is desired to improve the strength of the glaze. Sodium silicate of this type is similar to that sold on the market as N brand by Phladel-v.

Thereafter the material. is f pressed through a screen to subdivide the massintopellets of a size determined by the screen mesh. 'Ihis operation and a subsequent tumbling action serves to cover practically the entire surface`of the pellets witha coating `of laminae initially bonded thereto with the liquid mixed with the material. This treatment also gives the pellets a somewhat special shape.v

The pellets are then preferably dried under heat to evaporate. water'from the sodium silicate.

centrate at the surface of the pellets. 'I'hereafter the pellets are heated to temperatures lof 4about y1200 to 14oo F. te convert the silicate into an insoluble form which in conjunction with the vermiculite forms a hard coating or glaze whichvery substantially reinforces the pellets and enables them to 'withstand rough treatment without crushing or disintegration. Vermiculite thus treatedweighs about -iifteen pounds Per.

cubic foot.

Very small Aparticles of exfoliated vermiculite which would otherwise have -little value mayy advantageously be'used, inasmuch as the sodium silicate initially` has a binding action which enableszthe formation of the larger pellets from individually smaller particlesv of exfoliated vermiculite... Such smallerl particles contain a large number of individual laminas of -small size which during `the treatment substantially cover'the pellets, thereby cooperating with .l

to provide the aforesaid the hardened coating reinforcement.

, Other glazing agents referred-'to in the ceramic trades as boronsf' such as salt cake, he. so-

vi'iium sulphate, whichl iluxunder heat to form` a glaze', may be used in' placeof` sodium silicate. l

The drawingillustratesdiagrammatieally one 'form'.ofapparatus for drying and heating lthe granules. It comprises an elongated rotary tube I0 inclined at an angle to cause the pellets to travel downwardly through the same at the proper rate-during rotation of the tube. The

readily conducted through its walls.

tube is supported and 'rotated at the proper inclination by rolls Il.

Before introduction into the tube the material is subdivided (after mixing with the coating liquid) into properly sized pellets, for example, by pressing" the same through a screen whose mesh determines the size of the particles. A V4 mesh screen. will form pellets of approximately 1A" size. As thus prepared the pellets are introduced into the upper end of the tube from a chute or hopper l2 discharging into the opening i3. The tumbling action received tends to form the material into roughly spherical pellets. During the drying action relatively low temperatures, i. er 200 to 400 F. should be maintained. .At these temperatures the silicate migrates to the surface of the pellets during the evaporation of the water. Such drying action takes place in the upper portions of the tube. As the dried pellets travel farther down the tube, they encounter increasingly higher temperatures until temf peratures from 1200 to 1400 F. are reached. These eii'ect the conversion of the coating or glazing material into the aforesaid hard coating or glaze. Such high temperatures may be produced by a heating chamber i4 surrounding the lower portion of the tube and containing gas or oil burners for developing high temperatures. The tube I is preferably metal and the heat is If the tube be made suiiiciently long, such, for example, as about thirty feet, the heat from the lowerheating zone may be allowed to travel upwardly through the tube to produce `the decreasing temperature gradient which at the upper end of the tube is from 200 to 400 F. The temperature gradient in the upper portion of the tube maybe controlled bythe amount of insulation l5 surrounding it.

At the lower end of the tube, the treated granules may be discharged upon a conveyer which may include a section I8 of metal belt on which the hot granules are cooled.

If the glazing agent has insuiilcient temporary bon'ding power to hold the material against disintegration during the sizing, tumbling and drying operations, it may be supplemented by some organic bonding material such as dextrine or pitch liquor. The latter are, of course, destroyed at the high temperatures reached but are suillcient to carry the material to the fusion zone. Obviously this invention is not limited to the details of the illustrative embodiment herein described since these may be variously modified. Moreover it is not indispensable that al1 features of the invention be used conjointly since various I tumbling the granules heating the same to moderate temperatures to dry the coating, then subjecting the granules while in separated condition to temperatures high enough to convert the coating into a thin insoluble reinforcing glaze around each granule, thereby to produce discrete reinforced granules of light weight.

PAUL S. DENNING. 

